Systems and methods are known that enable users to operate a pointing device to perform processing of an image using the pointer shown onscreen. For example, the user may draw a line or curve in the image by moving the pointing device accordingly.
In particular, it is known to facilitate the drawing of boundaries in medical images. A publication “Interactive Live-Wire Boundary Extraction”, by W. A. Barrett et al., Medical Image Analysis, 1(4):331-341, 1997, describes a tool which is said to allow accurate boundary extraction requiring minimal user input. Optimal boundaries are computed and selected at interactive rates as the user moves a mouse starting from a manually specified seed point. When the mouse position comes in proximity to an object edge, a “live-wire” boundary snaps to, and warps around the object of interest. It is noted that in order to facilitate seed point placement, a cursor snap is available which forces the mouse pointer to the maximum gradient magnitude pixel within a user specified neighborhood.
A problem of the above tool is that snapping the mouse pointer to a particular pixel in the image to establish a position in the image is inconvenient for a user.